The present invention relates to a rail pad for electrically isolating a railway rail from an adjacent rail fastening anchoring device (or shoulder) and a rail foundation.
In modern railway systems many electrical signals, for communication and rail traffic signalling purposes, are passed along railway rails. In order to prevent the conduction of such signals between the two rails, insulating rail pads are provided beneath the rail foot and insulators are provided between the rail foot and adjacent shoulders.
With the increasing use of steel sleepers such electrical insulation has become even more important. It is of course vital that such insulators function not only in dry conditions but also in wet conditions. A rail fastening assembly incorporating a standard rail pad is typically expected to have a wet electrical resistance of at least 5 k Ohms. However, some track operators require a far higher electrical resistance, for example 20 k Ohms.
According to a first aspect of the present invention there is provided a rail pad for electrically isolating a railway rail, the pad comprising a rail seat portion for supporting a foot of the rail, wherein the pad further comprises a pair of upstands joined to opposite edges of the rail seat portion of the pad by respective webs such that respective channels for directing water away from the rail are defined between the rail seat portion of the pad and each adjacent upstand.
Such a pad, which can be used on either discrete or continuous rail foundation, has an improved wet electrical resistance compared with prior art pads, since moisture falling on a rail fastening assembly in which the pad is used will be directed away from the assembly by the channels, in the manner of gutters. Moreover, electrical path length is increased.
When used on a railway sleeper such that the said channels run normal to the longitudinal axis of the rail foundation, the pad preferably overhangs at least one edge of the said rail foundation, thus directing moisture away from the rail foundation.
Such a pad desirably further comprises a lip provided on the underside of at least one of the edges of the pad which is to overhang the edge of the railway sleeper, allowing the pad to shed drips.
Desirably, the pad further comprises two pairs of spaced-apart tabs extending from opposite edges of the said pad alongside the said channels, each pair of tabs forming a recess therebetween for receiving a railway rail anchoring device, whereby the pad is located on the rail foundation.
Preferably, when used in a rail fastening assembly including electrical insulators, positioned between the rail and respective rail fastening anchoring devices, the height of each of the said upstands is such that the upstand overlaps the lower edge of the adjacent insulator, thereby further improving wet electrical resistance of the pad.
According to a second aspect of the present invention there is provided an assembly for electrically isolating a railway rail, the assembly comprising a rail pad in accordance with the first aspect of the present invention and an insulator for location between the rail and a rail fastening anchoring device, the insulator having a post portion which extends between the rail and the said rail fastening anchoring device, a lower edge of which post portion is formed with a downwardly-extending tab whereby when the insulator is in its operative configuration the tab is located within the channel of the rail pad.
Preferably, the length of the said tab is substantially equal to or greater than the width of the said rail fastening device.